KR20180038364A - Positive Electrode Active Material Particle Comprising Core Having Lithium Cobalt Oxide and Shell Having Composite metal Oxide Based Composition and Method of Manufacturing the Same - Google Patents

Abstract

Provided is a positive electrode active material particle comprising: a core containing lithium cobalt oxide represented by chemical formula 1, Li_aCo_(1-x)M_xO_(2-y)A_y: and a shell coated on a surface of the core, and containing composite metal oxide of a metal with an oxidation number of +2 and a metal with an oxidation number of +3. In the chemical formula 1, M is at least one selected from the group consisting of Ti, Mg, Zn, Si, Al, Zr, V, Mn, Nb, and Ni, A is oxygen-substituted halogen, and a, x, and y satisfy 1.00<=a<=1.05, 0<=x<=0.05, and 0<=y<=0.001.

Description

TECHNICAL FIELD The present invention relates to a positive electrode active material particle comprising a core containing lithium cobalt oxide and a shell containing a composite metal oxide and a method for producing the same. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive active material particle, Same}

The present invention relates to a cathode active material particle comprising a core comprising a lithium cobalt oxide and a shell comprising a composite metal oxide and a method for producing the same.

As the technology development and demand for mobile devices have increased, the demand for secondary batteries has increased sharply as an energy source. Among such secondary batteries, lithium secondary batteries having high energy density and operating potential, long cycle life, Have been commercialized and widely used.

In addition, as the interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, . Although nickel-metal hydride secondary batteries are mainly used as power sources for such electric vehicles and hybrid electric vehicles, researches using lithium secondary batteries having high energy density and discharge voltage are being actively carried out, and they are in the commercialization stage.

At present, LiCoO ₂ , ternary system (NMC / NCA), LiMnO ₄ , LiFePO ₄ and the like are used as a cathode material of a lithium secondary battery. Of these, LiCoO ₂ is expensive and has a lower capacity at the same voltage as the ternary system. Therefore, the use of ternary system is increasing to increase the capacity of the secondary battery.

However, in the case of LiCoO ₂ , since the advantages such as a high rolling density are also clearly present, LiCoO ₂ has been widely used up to now, and studies are under way to increase the operating voltage in order to develop a high capacity secondary battery.

However, in the case of the lithium cobalt oxide, when applying a high voltage for high capacity, more specifically, when applying a high voltage of 4.5 V or more, the amount of Li of LiCoO ₂ is increased and the surface becomes unstable and gas is generated due to a side reaction with the electrolyte , A swelling phenomenon occurs, and the stability is lowered, the possibility of structural instability is increased, and the lifetime characteristics are rapidly deteriorated.

To solve this problem, doping or coating a metal such as Al, Ti, Mg, or Zr on the surface of the LiCoO ₂ is a commonly used method. However, in the case of the coating layer made of the metal, the performance of the secondary battery may be deteriorated by interfering with the movement of Li ions during charging and discharging.

Therefore, there is a high demand for development of cathode active material based on lithium cobalt oxide which can be used stably at high voltage without deteriorating performance.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments, and have found that, as will be described later, the cathode active material particles contain lithium cobalt oxide; And a shell coated on the surface of the core and including a composite metal oxide of a metal having oxidation number of +2 and a metal having oxidation number of +3, and that the desired effect can be exhibited The present invention has been completed.

In order to accomplish the above object, the present invention provides a cathode active material particle,

A core comprising lithium cobalt oxide represented by the following formula (1); And

A shell coated on the surface of the core, the shell comprising a composite metal oxide of a metal having a oxidation number of +2 and a metal having a oxidation number of +3;

. &Lt; / RTI &gt;

Li _a Co _(1-x) M _x O _2-y A _y (1)

M is at least one member selected from the group consisting of Ti, Mg, Zn, Si, Al, Zr, V, Mn,

A is an oxygen-substituted halogen,

1.00? A? 1.05, 0? X? 0.05, and 0? Y?

Generally, when a lithium cobalt oxide is used as a cathode active material at a high voltage, a large amount of lithium ions are released from the lithium cobalt oxide particles, resulting in a crystal structure being deficient. As a result, an unstable crystal structure is collapsed and reversibility is lowered. In addition, when the lithium ion is Co ^{+ 3} or Co ⁴⁺ ions in the lithium cobalt oxide particle surface in the released state is to be reduced by the electrolyte, the oxygen is desorbed from the crystal structure of the above-described structure, the collapse is further promoted.

Therefore, in order to stably use the lithium cobalt oxide under a high voltage, even when a large amount of lithium ions are released, its crystal structure is stably maintained, and side reactions of the Co ions and the electrolyte must be suppressed.

Therefore, in the present invention, by forming a shell containing a composite metal oxide of a metal having a +2 oxidation number and a metal having a +3 oxidation end on the surface of a lithium cobalt oxide, compared with a conventional cathode active material particle containing only lithium cobalt oxide, It is possible to significantly reduce the reactivity to prevent elution of Co and prevent the problem of safety deterioration such as swelling due to gas generation and to suppress the change of the surface structure even under a high voltage to improve the structural stability of the cathode active material particles, And the shell also has a layered structure, so that the migration of lithium ions is relatively easy even in the shell, thereby effectively preventing a deterioration in the rate characteristic of the secondary battery

In one specific example, the thickness of the shell formed on the surface of the core may be between 5 nanometers and 100 nanometers, and in particular between 10 nanometers and 30 nanometers.

If the thickness of the shell is less than 5 nanometers, the ratio of the shell in the cathode active material particles may be excessively small and the desired effect may not be sufficiently exhibited. On the other hand, if the thickness of the shell is less than 100 nanometers The proportion of the shell in the positive electrode active material particles becomes excessively high and the overall capacity of the positive electrode active material is relatively decreased. In addition, the rolling density is lowered and the energy density per volume in the actual cell is lowered, It is undesirable because there is a problem of lowering.

Further, in one specific example, the shell may be coated in an area of 50% to 100% with respect to the surface area of the core.

When the shell is coated with an area of less than 50% out of the above range with respect to the surface area of the core, the coating area of the shell is too small and the desired effect is not sufficiently exhibited.

The composite metal oxide of the thus formed shell is in the form of a composite oxide of a +2-valent and a +3-valent metal, and may have a layered structure such as lithium cobalt oxide of the core.

Therefore, the shell containing the composite metal oxide prevents the elution of Co by suppressing the reaction that may occur due to the reaction with the electrolytic solution on the surface of the lithium cobalt oxide, secures the structural stability of the surface, The coating can act as a conductor of Li ions and can move the Li ions from the lithium cobalt oxide more smoothly, thereby preventing deterioration of the output characteristics.

Such a composite metal oxide may be represented by the following general formula (2) in one specific example.

M ' _t M'' _w O _u (2)

M 'is at least one metal selected from the group consisting of Co, Zn, Mg, Fe, Cu, and Ni as a metal having an oxidation number of +2,

M "is a metal having an oxidation number of +3 and is at least one selected from the group consisting of Al, Co, Ni and Fe,

(T + w) / u &lt; / = 0.8, u is determined according to the values of t and w.

More specifically, M 'may be Co, Zn, Ni, or Mg, and M' 'may be Al.

Thus, the oxide is in the process of the metal elements of the mixed metal oxide to be adsorbed to the lithium cobalt oxide particles _{surface, [M 't M''} w (OH) 2] having a layered structure represented by Formula 2 ^{q +} (X ^{n _{-) q / n · zH 2}} O ( wherein, X is the anion ^{_{Cl-, CO 3 2-, OH -}} . ^{_{comprises, NO 3-, SO 4 2-,}} PO 4 3-) to be formed, The anions such as X may exist in the layered structure in order to adjust the charge valence and then be partially or completely removed to form the composite metal oxide having a layered structure.

The cathode active material particle may further include an outermost surface layer coated on the shell and including a composite metal oxide of a metal having an oxidation number of +2 and a metal having a oxidation number of +3.

At this time, the composite metal oxide included in the outermost surface layer may be the same composition as the composite metal oxide included in the shell. In detail, at least one of the metals forming the outermost surface layer is a metal not included in the shell, The composition of the shell and the outermost surface layer may be different.

That is, the cathode active material particle of the present invention may also include a layered structure in which a layered composite metal oxide layer is laminated on one or more layers of a core of lithium cobalt oxide.

On the other hand, the present invention provides a method for producing the cathode active material particles,

(a) a metal salt containing M '(wherein M' is at least one metal selected from the group consisting of Co, Zn, Mg, Fe, Cu and Ni as a metal having an oxidation number of +2) , M &quot; is at least one selected from the group consisting of Al, Co, Ni and Fe as a metal having an oxidation number of +3);

(b) dispersing lithium cobalt oxide in a particulate state in a solvent and further mixing the solution for shell preparation; And

(c) filtering and drying the mixed solution, followed by heat treatment;

. &Lt; / RTI &gt;

According to the above production method, the cathode active material particle of the present invention is produced by first coating lithium cobalt oxide particles with a solution for making a shell, together with drying, and forming a composite metal oxide by the heat treatment in the step (c).

Specifically, in the process (b), in the process of adsorbing the metal ions of M ' ^{2 +} and M " ³⁺ onto the surface of the lithium cobalt oxide particles, [M' _t M" _w (OH) ₂ ] ^{q +} (X ^{n -} ) _{q / n} zH ₂ O wherein X is an anion and includes Cl-, CO ₃ ^2- , OH-, NO ^{3 -} , SO ₄ ^2- , PO ₄ ^3- . And the anions such as X are coated in a form existing between the layered structures in order to adjust the charge valence and are partially or wholly removed in the heat treatment process of the step (c).

Thus, the composite metal oxide forming the shell can be coated on the surface of the core in a layered structure by being coated on the surface of the lithium cobalt oxide particles forming the core in the precursor step, A continuous structure can be formed to form a structurally more stable shell, and a chemically more stable shell layer can be formed with a structure in which M ' ^{2 +} and M'' ^{3 +} metals are uniformly mixed.

The solvent used in the preparation of the shell preparation solution may be the same as or different from that of the solvent used in the preparation of the shell, Is more preferable.

In one specific example, the particle size (D50) of the lithium cobalt oxide in the particle state may be between 5 micrometers and 25 micrometers.

If it is out of the above range and less than 5 micrometers, it is difficult to control the lithium cobalt oxide particles because of difficulty in the process. If it exceeds 25 micrometers, it is preferable because there is a loss in terms of rolling density and capacity. not.

Furthermore, the method for producing the cathode active material particle, in which the cathode active material particle further includes an outermost surface layer,

(d) a metal salt containing M '(wherein M' is at least one metal selected from the group consisting of Co, Zn, Mg, Fe, Cu and Ni as a metal having an oxidation number of +2) , M "is a metal having an oxidation number of +3 and is at least one selected from the group consisting of Al, Co, Ni, and Fe); preparing a solution for forming an outermost surface layer;

(e) dispersing lithium cobalt oxide having a shell in a particle state in a solvent and further mixing the outermost surface layer forming solution; And

(f) filtering and drying the mixed solution, followed by heat treatment;

May be further included.

At this time, depending on whether the composition of the composite metal oxide contained in the outermost surface layer is the same as or different from the composition of the shell, the metal type of the metal salt contained in the solution for forming the outermost surface layer may vary.

Specifically, in the case of the same process, the same solution as the solution for preparing a shell can be used. In the case of different process, the M 'containing metal salt and the M' 'containing metal salt contained in the solution for preparing the outermost surface layer in the step (d) At least one of which contains a metal other than the metal salt contained in the solution for making a shell.

In the above manufacturing method, the pH of the mixed solution of the solution in which the lithium cobalt oxide is dispersed in the solvent and the solution for preparing the shell or the outermost coating layer can be maintained at 7 to 12, specifically 8 to 11.

If the pH of the solution is less than 7, the adsorption of the metal ions in the solution for preparation may not be performed uniformly, and the adsorbed metal ions may be eluted into the solution again, , And if the pH is higher than 12, the metal ions may precipitate in the form of hydroxide to prevent coating on the surface of the lithium cobalt oxide, which is not preferable.

On the other hand, the present invention provides another method for producing the cathode active material particle,

(a) a metal salt containing M '(wherein M' is at least one metal selected from the group consisting of Co, Zn, Mg, Fe, Cu and Ni as a metal having an oxidation number of +2) , M &quot; is at least one metal selected from the group consisting of Al, Co, Ni and Fe as a metal having an oxidation number of +3) to synthesize an M'-M &quot; complex hydroxide through a coprecipitation reaction process;

(b) mixing the particulate M'-M "complex hydroxide and the particulate lithium cobalt oxide; And

(c) heat-treating the mixture;

. &Lt; / RTI &gt;

According to the above production method, the cathode active material particles of the present invention are produced by first preparing a composite metal hydroxide as a precursor of a composite metal oxide to form a shell by coprecipitation reaction, mixing it with lithium cobalt oxide particles, And a composite metal oxide is formed on the oxide particle core.

Therefore, the composite metal oxide forming the shell can be coated on the surface of the core in a layered structure, while being adhered to the surface of the lithium cobalt oxide particles forming the core in the form of hydroxide in the form of oxides by heat treatment.

The above method can easily control the composition and structure of the complex oxide layer protecting the surface, and can form a composite oxide having a uniform lamellar structure on the surface of the core without being sensitive to the pH. It is possible to make the composition of the shell layer more uniform than the method using an aqueous solution.

In this case, the M'-M '' complex hydroxide synthesized in the above process (a) is [M ' _t M " _w (OH) ₂ ] ^{q +} (X ^{n -} ) _{q / n} zH ₂ O anions Cl-, CO ₃ ^2-, OH ^{-, _{and, NO 3-, SO 4 2-,}} PO 4 3- included, and 0.125≤t / w≤1 the, determined according to the value of the q are t and w ).

The shell-forming precursor in the hydroxide form is converted into an oxide form and can be more firmly attached to the surface of the lithium cobalt oxide particles.

Furthermore, in the above production method, in the case where the cathode active material particles further include an outermost surface layer on a continuous line,

(d) a metal salt containing M '(wherein M' is at least one metal selected from the group consisting of Co, Zn, Mg, Fe, Cu and Ni as a metal having an oxidation number of +2) , M &quot; is at least one selected from the group consisting of Al, Co, Ni and Fe as a metal having an oxidation number of +3) through a coprecipitation reaction to form a second M'- ;

(e) mixing a second M'-M "complex hydroxide in a particulate state with a lithium cobalt oxide having a shell in a particulate state; And

(f) heat treating the mixture;

May be further included.

At this time, depending on whether the composition of the composite metal oxide contained in the outermost surface layer is the same as or different from the composition of the shell, the composition of the composite metal oxide contained in the solution of the step (d) for forming the second M'- The metal type of the metal salt may be varied.

Specifically, in the case of using the same solution, the same solution as the solution for producing a hydroxide for shell formation can be used. In the case of differentiation, in the step (d) for forming the second M'- At least one of the M '-containing metal salt and the M' '-containing metal salt in the solution may contain a metal other than the metal contained in the solution of the metal salts contained in the solution of the step (a).

Here, the mixing ratio of the composite metal hydroxide formed by the coprecipitation reaction can be appropriately selected depending on the coating thickness.

Meanwhile, as described above, in order to produce the cathode active material particles according to the present invention in each production method, M '-containing metal salt and M' '-containing metal salt are used to form a shell or an outermost surface layer.

At this time, in the above solutions, the M '-containing metal salt and the M' '-containing metal salt can be mixed in a range that M' and M "are in a molar ratio and M '/ M" = 0.125-1.

If the M '/ M "ratio is out of the above range and is less than 0.125 or higher than 1, the layered structure is not formed and the M' containing metal salt or M '' containing metal salt is formed to form the shell Not possible is not desirable.

In one specific example, the type of the metal salt is not limited, and in particular, it may be at least one kind selected from a chloride, a sulfate, a carbonate, and a nitrate.

Further, in each of the manufacturing processes, the drying of the process (c) may be performed at 30 to 130 degrees Celsius for 1 to 24 hours, and the heat treatment of the process (c) or (f) Can be performed in the range of 1 to 100 degrees, more specifically, in the range of 700 to 1000 degrees for 1 to 10 hours.

If the drying in the step (c) is carried out at an excessively low temperature beyond the above-mentioned range, or if the drying is carried out for an excessively short time, the drying may not be performed properly. On the other hand, Is not preferable because a reaction that causes a change in structure may occur.

In addition, when the heat treatment in the steps (c) and (f) is carried out at an excessively low temperature beyond the above range, or when the heat treatment is performed for an excessively short time, the core-shell structure of the cathode active material particles may not be stably formed On the contrary, when the lithium-cobalt composite oxide is performed at an excessively high temperature or is carried out for an excessively long time, the physical and chemical properties of the lithium cobalt oxide and the composite metal oxide constituting the cathode active material particles may be changed, have.

In addition, the present invention provides a secondary battery comprising the positive electrode active material particles, the negative electrode and the electrolyte solution, and the kind of the secondary battery is not particularly limited, but specific examples include a high energy density, A secondary battery such as a lithium ion battery, a lithium ion polymer battery or the like, which has merits such as power, voltage, and output stability.

Generally, a lithium secondary battery is composed of a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt.

The positive electrode is prepared, for example, by coating a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector, and then drying the mixture. Optionally, a filler may be further added to the mixture.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component which assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode is manufactured by applying and drying a negative electrode active material on a negative electrode collector, and if necessary, the above-described components may be selectively included.

Examples of the negative electrode active material include carbon such as non-graphitized carbon and graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1 - x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separation membrane and the separation film are interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

Further, in one specific example, in order to improve the safety of a high energy density cell, the separation membrane and / or the separation film may be an organic / inorganic composite porous SRS (Safety-Reinforcing Separators) separator.

The SRS separator is manufactured by using inorganic particles and a binder polymer on the polyolefin-based separator substrate as an active layer component. In addition to the pore structure contained in the separator substrate itself, the SRS separator is formed by interstitial volume between inorganic particles And has a uniform pore structure.

The use of such an organic / inorganic composite porous separator has the advantage of suppressing an increase in thickness of the cell due to swelling at the time of chemical conversion compared with the case of using a conventional separator, When a gelable polymer is used when liquid electrolyte is impregnated, it can also be used as an electrolyte.

In addition, the organic / inorganic composite porous separator can exhibit excellent adhesion characteristics by controlling the contents of the inorganic particles and the binder polymer in the separator, so that the cell assembly process can be easily performed.

The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles usable in the present invention are not particularly limited as long as the oxidation and / or reduction reaction does not occur in the operating voltage range of the applied battery (for example, 0 to 5 V based on Li / Li +). Particularly, when inorganic particles having an ion-transporting ability are used, the ion conductivity in the electrochemical device can be increased and the performance can be improved. Therefore, it is preferable that the ionic conductivity is as high as possible. In addition, when the inorganic particles have a high density, it is difficult to disperse the particles at the time of coating, and there is a problem of an increase in weight during the production of the battery. In the case of an inorganic substance having a high dielectric constant, dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte also contributes to increase ionic conductivity of the electrolyte.

The lithium salt-containing non-aqueous electrolyte is composed of an organic electrolytic solution and a lithium salt. As the organic electrolytic solution, a non-aqueous liquid electrolytic solution, an organic solid electrolyte, an inorganic solid electrolyte and the like are used.

Examples of the nonaqueous liquid electrolytic solution include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI- LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO _{4 -} LiI-LiOH and Li ₃ PO _{4 -} Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

Further, the non-aqueous electrolyte solution containing a lithium salt may include electrolyte additives, and the electrolyte additives may be selected from the group consisting of ethylene carbonate, vinyl acetate, vinylethylene carbonate, thiophene, 1,3-propane sultone, succinic anhydride, Wherein the denitrile additive may be at least one of malononitrile, succinonitrile, glutaronitrile, adiponitrile, and phthalonitrile.

In addition, for the purpose of improving the charge-discharge characteristics and the flame retardancy, there can be mentioned, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexaphosphoric triamide, , Sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol and aluminum trichloride. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

The present invention also provides a battery pack including the secondary battery and a device including the battery pack. Since the battery pack and the device are known in the art, a detailed description thereof will be omitted herein. do.

As described above, the cathode active material particle according to the present invention comprises a core containing lithium cobalt oxide; And a shell coated on the surface of the core and containing a composite metal oxide of a metal having an oxidation number of +2 and a metal having a oxidation number of +3, compared to a conventional cathode active material particle containing only lithium cobalt oxide, Due to the surface protective effect of the lithium cobalt oxide, the reactivity with the electrolytic solution is remarkably reduced, so that the problem of the safety deterioration such as the swelling phenomenon due to the generation of the gas can be prevented and the change of the surface structure can be suppressed even under a high voltage. It is possible to improve the structural stability of the positive electrode active material particles and improve the lifetime characteristics of the secondary battery. Since the shell also has a layered structure, the movement of lithium ions is relatively easy even in the shell, It is possible to effectively prevent deterioration of characteristics.

1 is an SEM photograph of a cathode active material particle according to Example 1 of the present invention;
2 is an SEM photograph of a cathode active material particle according to Example 2 of the present invention;
3 is a graph comparing life characteristics at 25 ° C according to Experimental Example 2 of the present invention;
4 is a graph comparing lifetime characteristics at 45 DEG C according to Experimental Example 2 of the present invention

Hereinafter, the present invention will be further described with reference to Examples of the present invention, but the scope of the present invention is not limited thereto.

&Lt; Example 1 >

Particulate LiCoO ₂ particles having a particle diameter ranging from 10 to 20 micrometers Was dispersed in 1000 ml of water and a solution of CoCl ₂ and Al ₂ (SO ₄ ) ₃ in water at a molar ratio of Co: Al = 1: 2 was added so that (Co + Al) was 5000 ppm relative to LiCoO ₂ And mixed with a zirconia ball using a ball mill. The mixture (pH = 10) was filtered, dried at 130 ° C, and fired at 1000 ° C for 5 hours in an air atmosphere to synthesize a core-shell structure having a shell thickness of 10 nm. An SEM photograph of the synthesized active material is shown in Fig.

Referring to Figure 1, it is shown that in CoAl ₂ O ₄ of the layered structure matches the layered structure and the structure of LiCoO ₂ is formed on the surface, it can be seen that attached to the surface.

&Lt; Example 2 >

Co-Al-based hydroxide (CoAl ₂ (OH) ₈ ) was prepared by co-precipitation of sodium hydroxide with a solution of CoCl ₂ and Al ₂ (SO ₄ ) ₃ in 500 ml of water in a molar ratio of Co: ) Were synthesized.

100 parts by weight of LiCoO ₂ in a particle state in which the particle diameter is distributed in a range of 10 to 20 micrometers, 100 parts by weight of CoAl ₂ (OH) ₈ And then fired at 1000 ° C for 5 hours to synthesize a core-shell structure active material having a shell thickness of 10 nm containing CoAl ₂ O ₄ . An SEM photograph of the synthesized active material is shown in Fig.

2, unlike Example 1, a CoAl ₂ O ₄ coating is formed on a LiCoO ₂ It can be seen that even distribution throughout the surface is observed, while it is present as a continuous layered coating layer with the LiCoO ₂ matrix.

&Lt; Comparative Example 1 &

LiCoO ₂ in the form of particles having a particle diameter in the range of 10 to 20 micrometers was used as the cathode active material particle.

<Experimental Example 1>

The cathode active material particles, the PVdF binder, and the natural graphite conductive material prepared in Examples 1 and 2 and Comparative Example 1 were thoroughly mixed in NMP to have a weight ratio of 95: 2.5: 2.5 (cathode active material: binder: conductive material) Thick Al foil, and dried at 130 DEG C to prepare a positive electrode. Lithium foil was used as the cathode, and half-coin cells were prepared using an electrolyte solution containing 1M of LiPF ₆ in a solvent of EC: DMC: DEC = 1: 2: 1.

A plurality of half-coin cells thus manufactured were charged and discharged at 0.1 C and 0.5 C / 1 C in a CC / CV charging mode with an upper limit voltage of 4.55 V and a lower half-voltage 2.5 V CC discharge mode at 25 ° C. and 45 ° C., The life characteristics were evaluated, and the results are shown in Figs. 3 and 4.

Referring to FIGS. 3 and 4, it can be seen that the stability of the surface is improved even at a high voltage of 4.55 V or more, and the capacity retention rate is 85% or more even for 50 cycles. On the other hand, in the case of the comparative example 1, the lifespan property rapidly drops to 70% or less before 40 cycles and the structural stability is completely lowered.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims (24)

A core comprising lithium cobalt oxide represented by the following formula (1); And
A shell coated on the surface of the core, the shell comprising a composite metal oxide of a metal having a oxidation number of +2 and a metal having a oxidation number of +3;
The positive electrode active material particles according to claim 1,
Li _a Co _(1-x) M _x O _2-y A _y (1)
M is at least one member selected from the group consisting of Ti, Mg, Zn, Si, Al, Zr, V, Mn,
A is an oxygen-substituted halogen,
1.00? A? 1.05, 0? X? 0.05, and 0? Y? The cathode active material particle according to claim 1, wherein the thickness of the shell is 5 nanometers to 100 nanometers. The positive electrode active material particle according to claim 1, wherein the shell is formed in an area of 50% to 100% with respect to a surface area of the core. The cathode active material particle according to claim 1, wherein the composite metal oxide of the shell has a layered structure. The positive electrode active material particle according to claim 1, wherein the composite metal oxide is expressed by the following formula (2)
M ' _t M'' _w O _u (2)
M 'is at least one metal selected from the group consisting of Co, Zn, Mg, Fe, Cu, and Ni as a metal having an oxidation number of +2,
M "is a metal having an oxidation number of +3 and is at least one selected from the group consisting of Al, Co, Ni and Fe,
(T + w) / u &lt; / = 0.8, u is determined according to the values of t and w. The positive electrode active material particle according to claim 5, wherein M 'is Co, Zn, Ni or Mg, and M "is Al. 2. The lithium secondary battery according to claim 1, wherein the cathode active material particle further comprises an outermost surface layer coated on the shell and including a composite metal oxide of a metal having an oxidation number of +2 and a metal having a oxidation number of +3 As a cathode active material particle. The positive electrode active material particle according to claim 7, wherein at least one of the metals forming the outermost surface layer is a metal not contained in the shell. 9. A method of producing a cathode active material particle according to any one of claims 1 to 8,
(a) a metal salt containing M '(wherein M' is at least one metal selected from the group consisting of Co, Zn, Mg, Fe, Cu and Ni as a metal having an oxidation number of +2) , M &quot; is at least one selected from the group consisting of Al, Co, Ni and Fe as a metal having an oxidation number of +3);
(b) dispersing lithium cobalt oxide in a particulate state in a solvent and further mixing the solution for shell preparation; And
(c) filtering and drying the mixed solution prepared in the step (b), followed by heat treatment;
Wherein the positive electrode active material particles have an average particle diameter of not more than 100 nm. The method according to claim 9, wherein the solvent of the step (b) is water. The method according to claim 9, wherein the particle size (D50) of the lithium cobalt oxide in the particle state is 5 micrometers to 25 micrometers. The method of manufacturing a cathode active material according to claim 9,
(d) a metal salt containing M '(wherein M' is at least one metal selected from the group consisting of Co, Zn, Mg, Fe, Cu and Ni as a metal having an oxidation number of +2) , M "is a metal having an oxidation number of +3 and is at least one selected from the group consisting of Al, Co, Ni, and Fe); preparing a solution for forming an outermost surface layer;
(e) dispersing lithium cobalt oxide having a shell in a particle state in a solvent and further mixing the outermost surface layer forming solution; And
(f) filtering and drying the mixed solution prepared in the step (e), followed by heat treatment;
Wherein the positive electrode active material particles further comprise a negative electrode active material. 13. The method according to claim 12, wherein at least one of the M '-containing metal salt and the M' '-containing metal salt contained in the solution for preparing the outermost surface layer of the step (d) contains a metal other than the metal contained in the solution for shell- Wherein the positive electrode active material particles have an average particle size of not more than 100 nm. 9. A method of producing a cathode active material particle according to any one of claims 1 to 8,
(a) a metal salt containing M '(wherein M' is at least one metal selected from the group consisting of Co, Zn, Mg, Fe, Cu and Ni as a metal having an oxidation number of +2) , M &quot; is at least one metal selected from the group consisting of Al, Co, Ni and Fe as a metal having an oxidation number of +3) to synthesize an M'-M &quot; complex hydroxide through a coprecipitation reaction process;
(b) mixing the particulate M'-M "complex hydroxide and the particulate lithium cobalt oxide; And
(c) heat-treating the mixture prepared in the step (b);
Wherein the positive electrode active material particles have an average particle diameter of not more than 100 nm. The method of claim 14 wherein the M'-M 'synthesized in the above step (a)' is the complex hydroxide _{[M 't M''w} (OH) 2] q + (X n-) q / n · zH 2 O ( Wherein X is an anion comprising Cl-, CO ₃ ^2- , OH-, NO ^{3 -} , SO ₄ ^2- , PO ₄ ^3- , 0.125 t / w 1, Wherein the positive electrode active material particles are formed on the surface of the positive electrode active material particles. 15. The method of manufacturing a cathode active material according to claim 14,
(d) a metal salt containing M '(wherein M' is at least one metal selected from the group consisting of Co, Zn, Mg, Fe, Cu and Ni as a metal having an oxidation number of +2) , M &quot; is at least one selected from the group consisting of Al, Co, Ni and Fe as a metal having an oxidation number of +3) through a coprecipitation reaction to form a second M'- ;
(e) mixing a second M'-M "complex hydroxide in a particulate state with a lithium cobalt oxide having a shell in a particulate state; And
(f) heat treating the mixture prepared in the step (e);
Wherein the positive electrode active material particles further comprise a negative electrode active material. 17. The method of claim 16, wherein at least one of the M 'containing metal salt and the M' 'containing metal salt in the solution of step (d) for forming the second M'- Wherein the positive electrode active material particles contain a metal other than the metal contained in the metal salts. The method of any one of claims 9, 12, 14, and 16, wherein the M 'containing metal salt and the M' 'containing metal salt have M' / M " = 1 to 8, based on the total weight of the positive electrode active material particles. The method of producing a cathode active material particle according to any one of claims 9, 12, 14, and 16, wherein the metal salt is at least one kind selected from a chloride, a sulfate, a carbonate and a nitrate . The method according to any one of claims 9, 12, 14, and 16, wherein the heat treatment in the step (c) or the step (f) is performed in a range of 600 to 1100 degrees Celsius for 1 to 10 hours Wherein the positive electrode active material particles have an average particle size of not more than 100 nm. A secondary battery comprising a cathode, a cathode, and an electrolyte containing the cathode active material particles according to claim 1. 22. The method of claim 21, wherein the electrolyte comprises an electrolyte additive, wherein the electrolyte additive is selected from the group consisting of ethylene carbonate, vinyl acetate, vinyl ethylene carbonate, thiophene, 1,3-propane sultone, succinic anhydride, And a nitrile additive, wherein the dinitrile additive is at least one of malononitrile, succinonitrile, glutaronitrile, adiponitrile, and phthalonitrile. A battery pack comprising a secondary battery according to claim 21. A device comprising a battery pack according to claim 23.

Images